Process for producing aromatics and diolefins from petroleum



y 1947- N. K! CHANEY 2,423,374

PROCESS FOR PRODUCING AROMATICS AND DIOLEFINS FROM PETROLEUM Filed May 1. 1943 3 Sheets-Sheet 1 RJURETOR A 7' TOR/V6 N. K. CHANEY July 1, 1947.

PROCESS FOR PRODUCING AROMATICS AND DIOLEFINS FROM PETROLEUM Filed May 1, 1943 3 Sheets-Sheet 2 f/vrz/v Ta/E Quwu-nb k -a G M ra/e/vsy Patented July 1, 1947 PROCESS FOR PRODUCING AROMATICS DIOLEFIN S FROM PETROLEUM Newcomb, K. Chaney, Moylan, Pa., assignor to The United Gas Improvement Company, a corporation of Pennsylvania Application May 1, 1943, Serial No. 485,299

10 Claims. (Cl. 260-668) The present invention relates to the vapor phase pyrolysis of petroleum oil for the production of valuable hydrocarbons.

The controlled vapor phase pyrolysis of petroleum oil is capable of yielding a very wide variety of hydrocarbon products. Among such products may be mentioned the saturated aliphatic compounds of which the parafiines methane, propane, butanes, pentanes, hexanes and higher homologues are examples; the mono-olefines, of which ethylene, propylene, butylenes, amylenes, hexylenes and higher homologues are examples; the diolefines of which the conjugated diolefines, butadiene, isoprene, piperylene, hexadiene and others are examples; the acetylenes, of which acetylene, vinylacetylene, are examples. There may be also produced a variety of aromatic hydrocarbons containing only nuclear unsaturation such as benzene, toluene, xylenes, naphthalene, methyl naphthalenes, anthracene, and others; as well as aromatic hydrocarbons containing other than nuclear unsaturation of which styrene, methyl styrenes, indene, methyl indenes, phenyl acetylene, readily heat polymerizable unsaturated aromatic hydrocarbons boiling above 210 C. and

others, are examples. -Various alicyclic hydrocar bons may also be produced of which cyclopenta diene, methyl cyclopentadiene, cyclohexene, cyclohexadiene, alkyl cyclohexadienes, and others are examples. Considerable quantities of hydrogen and carbon may also be produced depending upon the severit of the pyrolysis.

All of the above mentioned compounds as well as others may be produced under a given set of pyrolyzing conditions. The production of all of these compounds, however, is not equally favored by any one set of conditions of pyrolysis. The production of relatively high yields of certain of these compounds is favored by pyrolysis conditions which are relatively mild as compared with other pyrolysis conditions which favor the production of relatively high yields of other products.

For example. the production of relatively high yields of diolefines having four or five carbon atoms per molecule is favored by relatively mild conditions of pyrolysis as compared with the conditions which favor the production of high yields of aromatic compounds in general, and particularly such aromatic hydrocarbons as benzene and naphthalene. Conversely the relatively severe conditions of pyrolysis which favor high yields of aromatic compounds result in low, and in some cases even negligible, yields of such diolefines as butadiene, isoprene, and piperylene.

The yield of such an aromatic olefine as styrene and the yield of such an alkylated aromatic-hydrocarbon as toluene, for example, while not favored by such severe conditions of pyrolysis as favor the higher yields of benzene, are generally, however, favored by pyrolysis conditions of greater severity than those which favor the highest yields of a diolefine such as butadiene.

Also under pyrolysis conditions conducive to the higher yields of diolefines, such as butadiene, isoprene, piperylene and cyclopentadiene, not only are the yields of individual aromatic compounds such as benzene and toluene, for example, relatively low, but the quality of individual aromatic fractions of the products of pyrolysis is also low due to contamination with parafiine and aliphatic olefine material of neighboring boiling point characteristics.

At the present time, certain of the above mentioned hydrocarbon products have assumed great strategic importance. For example, butadiene, the yield of which is favored by relatively mild pyrolysis conditions; styrene and toluene, the yields of which are favored by more severe pyrolysis conditions; and benzene the yield of which is favored by still more severe pyrolysis conditions;

are all in great demand as war materials. Buta-- diene and styrene are both employed as raw materials for synthetic rubber, while benzene is in great demand as a raw material in the production of high octane aviation motor fuel. Toluene is used as a raw material in the production of the important war explosive TNT.

Other diolefines such as isoprene and piperylene may very possibly develop great strategic importance in the production of synthetic rubber compositions, while-other aromatic hydrocarbons may have very valuable uses as rubber plasticizers as well as other uses as solvents for other materials of strategic importance.

The present invention is particularly addressed to the provision of a method of pyrolysis of petroleum oil and fractions thereof in the employment of which both a relatively high yield of diolefines, such as butadiene, isoprene, piperylene, and cyclopentadiene. and a relatively high yield of aromatic hydrocarbons of good quality, such as benzene, toluene, xylene, and styrene may be secured.

According to the present invention, a petroleum oil or a fraction thereof is subjected to stage-wise pyrolysis consisting of at least two pyrolyzing stages.

In one stage, the oil is subjected to decomposition in a pyrolytic environment which is of rela. tively low severity as compared to that of a succeeding stage. and in which conditions of pyroylsis are maintained such as to favor the production otfa relatively high yield of C4 and/or C5 diolefines and preferably a high yield of butadiene.

The products or this stage or pyrolysis are subjected to treatment for the removal of butadiene and/or other dioleilnes of neighboring boiling points therefrom, and the remaining products of pyrolysis or a selected fraction or fractions thereof are subjected to pyrolysis in a succeeding stage under pyrolytic conditions favorable to the production of a relatively high yield of aromatic hydrocarbon material and/ or aromatic hydrocarbon material of good quality, the latter particularly with respect to paraffinic contamination of neighboring boiling point characteristics.

The pyrolysis in any or all stages may be effected either in a continuous manner as is customary in tube cracking or cyclicly, as is customary in regenerative apparatus, such as apparatus for the production of oil gas or carburetted water gas.

Inasmuch as the invention may be performed in a very wide variety of apparatus, and with a wide variety of feed stocks, it is not at all desirable to employ the usual criteria of temperature, time of contact, etc.. as measures of the intensity (or depth or degree) of pyrolysis.

Intensity of pyrolysis depends on many factors such, for instance, as true temperature of the vapors and gas undergoing pyrolysis, the effectiv time of contact, the concentration of vapors of the oil, and any added hydrocarbon material, the presence of catalysts and possibly other environmental conditions.

True temperature, for example, may vary from the observed temperature according to some function of the factors influencing effective time of contact which in turn may vary from calculated time of contact depending on functions of space velocity, turbulence, and the surface-volume relationships of the cracking vessels. True temperature may also vary from observed temperature because of factors involving the pyrometers employed and their positions in relationship to the lining or other heat storage materials in the cracking vessels. It is obvious that many permutations of these factors may be made.

It is therefore highly desirable to employ other criteria as measures of the intensity of cracking,

which are more universal in their application,

and are much less subject to modification as a result of the particular apparatus employed.

Such an index of the intensity of cracking may be derived from the quantities of selected materials produced by the pyrolysis, for example, the

quantity of residual oil gas produced per unit of oil pyrolyzed (the derivation of which will be hereinafter described) may be employed as such an index.

As another example, there may be employed as such an index the ratio of the total quantity per unit of oil pyrolyzed of a product, the yield of which tends to increase with increasing severity of cracking, to the total quantity per unit of oil pyrolyzed of a. product, the yield of which tends to decrease with increasing intensity of cracking such, for example, as the ratio of the total quantity of benzene produced to the total quantity of butadiene produced.

A third example of such an index of intensity of pyrolysis is the proportion of paraffinic material contained in a selected normally liquid fraction of the products of pyrolysis such, for example, as the proportion by volume of parafiinic material contained in a toluene fraction of the products of pyrolysis, said fraction made after acid washing to remove oleflnic material and having a boiling range of 3 C., with the first drop not lower than 107.5 C. and the dry point not higher than 112.5" C.

Of the above mentioned indices, the first two. namely, the quantity of residual oil gas produced per unit of oil pyrolyzed and the ratio of the quantity of benzene produced per unit of oil pyrolyzed to the ratio of the quantity of butadiene produced per unit of oil pyrolyzed, increase with increasing intensity of cracking. The third of the above indices, namely, the proportion of paraflini material contained in a selected aromatic fraction of the products of pyrolysis decreases with increase in intensity of cracking.

Preferably the pyrolysis is conducted under conditions conducive to relatively homogeneous and relatively uniform" cracking. Homogeneous cracking is defined herein to embrace conditions such, for instance, as concentration of oil vapors, space velocity, turbulence, surface-volume relationships of the interior of the cracking vessel or vessels and character of heated surfaces which are such that in any given plane normal to the flow of materials, the materials throughout the plane have previously had substantially the same opportunity to be heated and to undergo the alternate decompositions and syntheses which comprise cracking and which progress toward products of greater thermal stability under the environment obtaining.

Other conditions being fixed, variation of any one of the following factors in the direction cited is considered to tend toward less homogeneity inthe cracking operation; (1) decreased surface/volume ratio of the cracking vessels beyond the vaporizing zone; (2) reduced atomization of the oil; (3) increased impingement of oil on highly heated surfaces prior to vaporization; (4) increased concentration of the oil vapors; (5) decreased turbulence; and (6) increased space velocity except as effecting turbulence.

By relatively uniform cracking is meant the absenc of wide variations in the intensity of cracking with respect to time. For example, in a cyclic operation in which oil cracking chambers are heated during a heating period and the stored heat utilized during the cracking period, the quantity of oil gas produced (and the yields of the desired products) per gallon of oil during any individual oil-cracking run will vary somewhat as the temperature of the cracking environment decreases during said run. The degree of variation will depend among other factors, upon the length of the oil-cracking run, the feed rate of oil charge stock and any hydrocarbon additives. the feed rate of any diluent or diluents such as steam, the presence or absence of supplementary heating during the run, the quantity of heat stored during the heating period and the character of the heat storage material.

Very large swings in oil gas production during a cycle are not preferred as any swing in oil gas production during a cycle necessitates a departure from the optimum conditions within the range of ployment of highly conductive heat storage ma terial.

Therefore, the environment of oil pyrolysis hereunder is advantageously arranged to provide not only relatively homogeneous cracking but also relatively uniform cracking.

Residual oil gas" is defined as the uncondensed final gas (composed of hydrocarbons and hydrogen) after removal of substantially all water vapor or after correction for the presence of water vapor, and after the removal of substantially all hydrogen sulfide or after the correction for the presence of hydrogen sulfide (unless the oil is low in sulfur content in which case the hydrogen sulfide is negligible for calculation of residual oil gas), and after removal of substantially all hydrocarbons having more than three carbon atoms, or after correction for the presence of such hydrocarbons having more than three car bon atoms, and after correction for the presence of gas not derived from the total hydrocarbon material cracked (oil plus any added hydrocarbon material to be pyrolyzed), such as air, and combustion gases from fuel used for heating, and after correction for the presence of any water gas which may be present even though derived in part from the hydrocarbon material cracked. Procedure for making such corrections will be set forth in detail hereinafter.

The residual gas remaining after the above removal or correction will be referred to herein and in the claims as residual oil gas.

Thus residual oil gas includes gas derived not only from the petroleum oil pyrolyzed but also gas other than water gas derived from any added hydrocarbon material under the conditions of said pyrolysis.

The desired intensity of cracking as measured by any of the above recited criteria can be arrived at by the adjustment of the oil pyrolyzin environment, including such factors as (1) temperature, and (2) efiective time of contact to obtain a desired intensity of cracking.

Various procedures for the control of temperature in cyclic gas-making sets are well understood by the skilled gas-maker. These include 1) adjustment of the length of the blast run; (2) adjustment of the rate of fuel consumption during the blast run; (3) adjustment of the length of the blast runwith respect to the gas-making run or runs; (4) adjustment of the length of the purge or purges; (5) adjustment of the volume of steam or other gas used for purging; (6) adjustment of the length of the cycle; (7) the use of a reverse run or runs and the adjustment of their length; (8) the use of a reverse purge or purges,- (9) the use of auxiliary heating means; (10) adjustment of the point of entry of secondary air and any tertiary air during the blast; and so forth.

In non-cyclic operation such as in continuous operation, for example, in tube cracking the control of temperature may be effected by any means known in the art.

Time of contact in cyclic apparatus may be controlled by various factors, one of which is, of course, the dimensions including cross-sectional area, free space and length of the gas-making path of the set. In a given set the length of the gas-making path is more or less fixed and the same applies to the diameters of the various parts thereof such as the diameter of the interior of the carburetter, the diameter of the connection between the carburetter and the superheater, and the diameter of the superheater. With a given rate of oil, added talisman-arms. 1: used,

and steam or other diluent, if used, the time of contact "may-.beincreased and decreased with increase and decrease respectively of the'free space through which the vapors flow, for example, by adjusting the quantity and arrangement of the checkerbrick employed.

Time of contact may also be adjusted by ad the rate at which the total hydrocarbon material is cracked, and the degree of the cracking are also important factors.

Then too, the point or points of admission of the material to be pyrolyzed, n the p t or points of steam and/or other diluent admission, if used, are to be considered.

Thus it will be seen that, although any exact mathematical determination of time of contact would be extremely involved, the control of the oil, added hydrocarbon material if used, and steam or other diluent rates, if used, the control of the point or points of entry of oil, added hydrocarbon material, if used, and steam or other diluent, if used, and the control of the amount and arrangement of checkerbrick, each alone or in combination affords to the skilled gas-maker a fairly flexible control of time of contact.

All such factors will be well understood by the skilled gas-maker, making it possible for him, upon becoming familiar with this invention, to readily adjust the operation of his set to yield the desired quantity of residual oil gas.

The foregoing observations with respect to time of contact apply equally to tube cracking with the exception that checkerbrick are usually rarely, if ever, employed, though provision may be made for some kind of filling.

Cracking in the first stage is usually preferably carried out in at atmosphere diluted with any suitable diluent gas which is preferably readily condensible such as steam and which is preferably present in sufficient quantity to materially reduce the partial pressures of the oil vapors. Diluent may be supplied in any suitable ratio such as from 4 parts of steam to 1 part of oil by weight to one part of steam to 2 parts of oil by weight. Still more preferably, at least 3 parts of steam to 2 parts of oil by weight are employed. When employing a diluent other than steam an equivalent volumetric ratio of diluent is preferred.

Higher ratios than those given may also be employed. High steam ratios tend to increase the yield of dienes, whereas low steam ratios do not favor as high a yield of dienes.

The use of water gas in large quantities as a diluent is preferably avoided among other reasons because of its relatively high concentration of hydrogen. Thus, it is preferred to restrict the presence of any blue water gas to below 35 cubic feet per gallon of oil pyrolyzed and more preferably to below 25 cubic feet per gallon of oil pyrolyzed, said cubic feet being taken as if measured at a pressure of 760 mm. and a temperature of 60 F.

Other things being equal, it is preferred in the first stage of pyrolysis to secure the relatively mild intensity of cracking desired by the combined influence of a relatively high temperature, short time of contact and high dilution rather than to secure the same intensity of cracking by the use of relatively low temperatures, relatively long time of contact and/or relatively low dilution. As a general observation, temperatures between 1400 and 1800 F., together with times of contact between one second and one tenth of a second together with diluents equivalent to those produced by the additions of from 1 to 4 pounds of steam per pound of oil are preferred subject to the condition that the intensity of cracking produced by the influence of these and other factors falls within the limits of the criteria for intensity of crackinghereinafter set forth.

In the second stage in which it is desired to produce a relatively high yield of aromatic hydrocarbons and/or aromatic hydrocarbon of high quality, it is preferred to secure the desired intensity of cracking by a combination of relatively low temperature, relatively long time of contact, and relatively low dilution, rather than producing this desired intensity by the combination of high temperatures, short times of contact and high dilution.

As a general observation, temperatures below 1600 F., times of contact of greater than one second, for example, from 1 to 8 seconds, and dilutions lower than that produced by the presence of one pound of steam per one pound of total hydrocarbon feed stock are preferred subject to the condition that the intensity of cracking produced by the influence of these and other factors satisfies the hereafter criteria for second stage pyrolysis.

More preferably in the second stage, less diluent is employed than that equivalent to 0.4 lb. of steam per lb. of total hydrocarbon feed stock. The higher times of contact are particularly preferred if a high yield of benzene is especially desired,

More particularly, in the practice of my invention the first stage comprises the pyrolysis of a petroleum oil or a fraction or fractions thereof in vapor phase preferably in the presence of a readily condensible diluent gas, such as steam, under conditions such that the residual oil gas as hereinafter more particularly defined is more than 20 cubic feet per gallon of oil pyrolyzed,

- more particularly more than 25 cu. ft., and still more particularly more than 30 cu. ft. per gallon of oil Dyrolyzed, and under conditions such that the ratio of total benzene produced to total butadiene produced is not greater than 2:1, more particularly not greater than 15:1, and still more particularly not greater than 1.3: 1.

Under such conditions of pyrolysis in the first stage of my process high yields of butadiene, isoprene, piperylene and cyclopentadiene, including optimum yields as well as high yields of desirable C4 and C5 mono-olefines, are obtainabl under conditions such that the remaining products, and particularly the products boiling in ranges embracing benzene, toluene and/or xylene are in a condition for the production of high yields and/ or high grade aromatic compounds in the second cracking stage.

The. quality of the aromatic compounds produced in the second stage may be conveniently measured by determining the paraffine content of a fraction of the products of pyrolysis, said fraction made after acid washing to remove olefines, and having a boiling range of 3 C., in: cluded between 107.5 C. and 112.5 C., and if greater purity is desired, having a boiling range of 1 C. including 110.7 C., the boiling point of toluene.

In accordance with my invention, the intensity of the pyrolysis in the second stage is at least sufficient to reduce the parafline content of said 3 C. fraction to below 4% by volume and preferably such as to reduce the parafiine content of said 1 C. fraction to or below 1% by volume. Any other convenient measure of aromatic quality equivalent to the above recited parafiin contents of the said 3 C. and said 1 C. toluene fractions may be employed in place thereof.

By the parafiine content is meant that determined in accordance with the Kattwinkle test set forth in the United States Army specification #501138-C dated February 6, 1942, which recites specifications for commercial and nitration toluene.

The above referred to acid washing for the removal of olefines may be performed by any suitable means known in the art, such as in accordance with the methods set forth (or by any equivalent method) in Gas Chemistry Handbook, 3rd edition, a publication of the American Gas Association, part III, pages 398 to 401, inclusive. It is preferred however to employ the Kattwinkle method of said above mentioned United States Army specification #50-1138-6 for the determination of paraflines instead of the paraifine determination method of said Gas Chemistry Handbook.

The total butadiene produced may be determined by isolating a C4 fraction from the products of first stage pyrolysis of a known quantity of oil by means of the well known Podbelniak apparatus. The butadiene content by weight of this fraction is determined by absorp ion in molt n maleic anhydride according to the method described by Tropsch and Mattox in Industrial and Engineering Chemistry, analytical edition, 6,

104 (1934) Any equivalent method of determination of the butadiene may be substituted.

The total benzene may be determined by analyz ing a sample of first stage condensate containing substantially all of the benzene produced from a known quantity of oil. The sample may be analyzed for its content of benzene by weight, in any suitable manner, such as by first freeing the sample of conjugated diolefines by contact with maleic anhydride, and then employing the Pona analysis--U. O. P, method No. 1-1-173-40, described in U. 0. P. Laboratory Test Methods for Petroleum and Its Products," a publication of the UniversalOil Products Company, Chicago, Illinois.

A method of determining Residual oil gas will be given hereinafter.

For convenience, the invention will be further illustrated in connection with the drawings which form a part of this specification and illustrate apparatus in which the invention may be conveniently performed, and in which:

Figure 1 shows an elevation partly in section. diagrammatically illustrating a cyclic gas-making set;

Figures 2 and 3 which figures when arranged end to end comprise a continuous flow sheet illustrate means for recovering valuable hydrocarbons from the gas produced.

Figure 4 is an elevation partly in section diagrammatically illustrating a continuous gas making set. 1 Referring to Figure 1: This figure illustrates diagrammatically apparatus in which the invene may be performed and comprises a cyclic gas-making set.

I indicates a generator, 2 is a carburetter, 3 is a with means for supplying fluid fuel such as tar,

generally indicated at 6, and with means for supplying air for combustion of the fuel generally indicated at l. The generator may be provided with secondary air supply means as at 8. 9 indicates checkerbrick arranged above the combustion space l0. ll, i2, and I3 are steam supply pipes.

The generator I is connected at its upper portion to the upper portion of the carburetter. 2 by connection I4. The carburetter is illustrated as devoid ofjcheckerbrick and is provided with oil supply means l5 and l5b provided with nozzles I6 and 16b respectively preferably capable of finely atomizing the oil. The carburetter is illustrated as also provided with added hydrocarbon material supply means I51: and [50 provided with nozzles [6a and I60 respectively.

The carburetter 2 is connected at its base with the base of the superheater 3 by connection H.

The superheater 3 is shown provided with the checkerbrick indicated conventionally at l8. Off-.

take ,I 9 provided with valve 20 leads from the top of the superheater to the wash box 4, from whence connection 20a. provided with valve 2| leads to condensat recovery equipment and a gas relief holder (not shown).

The superheater is further provided with a stack valve 22 and may be provided with a steam supply means such as steam pipe 23. Air supply means such as 24 may be provided for admitting tertiary air to the superheater.

The generator i may be provided with the gas ofitake 25 provided with valve 26 and leading from the lower portion .of the generator i to the wash box 4.

The refractory linings of the carburetter chamber and the superheater indicated at 21 and 28 respectively, as well as the checkerbrick such as in the superheater may if desired be of carborundum or other highly heat conductive material instead of the clay fire brick customarily employed for this purpose. The use of relatively highly heat conductive refractory material, an outstanding example of which is carborundum or silicon carbide, is especially advantageous from the standpoint of obtaining uniformity of cracking since among other things the swing in temperature during any given cycle is thus considerably reduced as compared to the swing when clay fire brick is used.

The carburetter may be provided with checkerbrick as well as the superheater. Checkerbrick in the carburetter if employed may be flued or staggered.

Checkerbrick or its equivalent is preferred in the superheater.

Other fluid fuel than tar may be employed for heating the generator I, such for instance, as oil or gas. Further, the generator may be provided with a grate and solid fuel burned thereon for heating'instead of fluid fuel, if desired.

Thermocouples'such as the shielded thermocouples 29, 30, 3|, 32 and 33' may be provided at spaced intervals through the vaporizing and cracking chambers, their connections leading to temperature recorders (not shown).

An illustrative cycle of operation of the apparatus of Figure 1 will be given.

In operation of the apparatus of Figure 1, fluid fuel such as tar, oil or gas is admitted to the generator burner 5 and burned in the generator, with air supplied through pipe I. Secondary air may be supplied through air supply pipe 8. The burning products pass from the enerator to the carburetter 2 by way of connection l4 and thence through carburetter to the superheater by way of connection I I. Tertiary air may be supplied through air supply means 24, if desired. The combustion products pass through the superheater and through the stack, valve 22 to atmosphere or to a waste heat through thestack valve 22.

After the set is purged, the stack valve 22 is closed, valve 26 is closed. and valves 20 and 2| are opened.

The set, is now in condition for the continuance of a cycle of either first stage or second stage operation.

In first stage operation a petroleum oil is admitted to the carburetter in finely atomized condition and preferably by the nozzle lBb into the void space of the carburetter.

Additional hydrocarbon material may if desired be admitted to the carburetter during the oil admission and atomized by the nozzle 16c.

Alternatively oil and added hydrocarbon admission means I5 and l5a provided with nozzles l6 and Mia respectively may be employed instead of means I51) and l5c or together therewith.

On the other hand either one of the oil or added hydrocarbon material may be admitted to the top of or bottom of the carburetter with the other admitted at the bottom'or top.

Such hydrocarbon material may be of any suitable character, such as one or more f the products of the pyrolysis of petroleum oil, either aromatic or non-aromatic and particularly nonaromatic, Examples are aliphatic hydrocarbon material having 4, 5 and/or 6 carbon atoms to the molecule such as butanes, pentanes, hexanes,.butylenes, amylenes and hexvlenes.

' Simultaneously with the admission of oil and added hydrocarbon (if employed) steam is admitted to the generator through the steam supply |3 in the generator base, heated in passage through the generator checkerbrick and passed into the carburetter top by way of connection l4. A portion or all of the steam may be admitted through the steam supply means l2 at the generator top above the checkerbrick, instead of through I3 at the bottom, and/or the temperature of the steam may be controlled by proportioning the quantities admitted to the two portions of the generator.

If desired, the added hydrocarbon material, if 2 employed, in' whole or in part, may be mixed with the oil and admitted therewith through supply means l5, or otherwise.

The oil and added hydrocarbon material, if employed, are vaporized in the carburetter in the presence of the superheated steam from the generator, the quantity of steam being sufficient to materially reduce the partial pressure of the oil vapors.

(if employed), and steam pass from the carburetter into the superheater through connection" I1. Some cracking may take place in the carbu-f retter.

From the base of the superheater the vapo rized hydrocarbons, steam and partially crackedhydrocarbon vapors pass upward through the superheater checkerbrick in which the desired pyrolysis is completed. 1

The reaction products and steam pass through connection IS, the wash box 4, and connection 20 to a relief holder (not shown), and thence through condensing or other apparatus (not shown) for the removal of the desired products fromthe gas. I

After this operation, termed the run, the admission of oil and added hydrocarbon material, if used, may be discontinued and the reaction products purged from the set by steam admitted to the generator, the reaction products being purged into the relief holder through the wash box.

The cycle may then be repeated. The above cycle is merely illustrative, it may be very greatly modified. For instance, a back run with steam or steam and oil-or steam and oil and added hydrocarbon material may be made during the cycle, with steam or steam and oil or steam and oil and added hydrocarbon material supplied, for

example, through supply means 23. In such case,-

the stack-valve 22 is closed, valve 20 is closed and valve 26 open. The steam or steam and oil or steam and oil and added hydrocarbon material vapors and reaction products pass reversely through the superheater, carburetter and generator and through connection 26 to the wash box and to the relief holder (not shown).

The fluid fuel burner as a means of providing heat during the blow is preferred, but recourse might be made to the use of a solid fuel bed as in the conventional water gas generator, with the difference that it is preferred not to pass any large quantity of water gas through the carburetter and superheater during the oil cracking period. Other means for superheating steam for the process might be then employed or saturated steam employed. The use of superheated steam, however, is preferred as it reduces the heating load on the carburetter.

During the blow, the operation is conducted to obtain the desired distribution of heat throughout the carburetter and superheater.

The temperature gradient throughout the set will vary with operating conditions and the nature and size of the set lining and checkerbrick or other heat storage material.

In the case of set lining and other refractory material present, this is in a measure associated. with the relative heat conductivity thereof. For instance, the substitution of refractory brick made of silicon carbide for refractory brick made of ordinary fire clay will shift the temperature gradient of the set and other conditions being equal will reduce the temperature swing throughout the cycle.

The temperature gradient naturally set up by 'the blow may be modified prior to the run if desired.

The point or points of introduction of the oil and/or added aromatic hydrocarbon material may vary in different gas making equipment, from those chosen for illustration.

As previously pointed out, having selected a given petroleum oil, or a fraction thereof, its

. 12 pyrolysis is controlled by the gas maker (modifying the interior of his set in accordance with the above observations it he finds it necessary or desirable), such that (1) ratio of the benzene produced to the butadiene produced does not exceed the certainmaxima given above, and (2) the residual oil gas exceeds the certain minima given above.

Methods for the determination of the quantities of butadiene and benzene per gallon of oil pyrolyzed'i-liave already been given heretofore.

As previously stated the first stage of the present invention includes adjusting the oil pyrolyzing environment including such factors as temperature, effective time of contact and concentration of oil vapors so that per gallon of oil the total volume of residual oil gas" produced after the removal of substantially all water vapor, or after correction for the presence of water vapor; and after the removal of substantially all hydrogen sulfide, or afterv the correction for the presence of hydrogen sulfide (unless the oil is low in sulfur content, in which case the hydrogen sulfide is negligible for calculation of residual oil gas); and after removal of substantially all hydrocarbons having more than three carbon atoms, or after correction for the presence of hydrocarbons having more than three carbon atoms; and after correction for the presence of gas not derived from the total hydrocarbon material cracked (petroleum oil plus added aromatic hydrocarbon material) such as air, and combustion gases from fuel used for heating and after the correction for the presence of any water gas which maybe present even though derived in part from the hydrocarbon material cracked; is maintained above 20, and preferably above 25, and more preferably above 30 cubic feet taken as if measured at a pressure of 7.60 mm. and a temperature of F.

The removal from the gas of hydrocarbons by condensation may be accomplished by any suitable means.

Generally speaking, there are four tools available for this purpose, namely, refrigeration, compression, absorption, such as in a scrubbing oil, and adsorption, such as on activated carbon. These may be used singly or in any desired combination.

As before stated, the object of the first stage operation is to produce a higher yield of diolefine hydrocarbon material of 4 and 5 carbon atoms and particularly a higher yield of butadiene than accompanies the production of aromatic hydrocarbons in high yield and/or of high quality.

Therefore, prior to the employment of first stage pyrolysis products as second stage feed stock, the desired diolefine material is removed therefrom with or without the removal of other selected hydrocarbon material as desired.

The second stage feed stock may comprise any desired portion of the products of pyrolysis of the first stage remaining after the removal of the desired diolefine and other selected material. The second stage feed stock may therefore include normally gaseous first stage products as well as normally liquid material. On the other hand such fractions of the first stage products may be employed as, for example, a fraction boiling between 60 C. and C., or between 90 C. and C., or between 125 C. and 0., or between 60 C. and 165 C. or closer cuts thereof embracing the boiling points of the individual aromatic hydrocarbons benzene, toluene,

13 and the xylenes. Any combinationot such fractions may be employed together with or without additional hydrocarbon material not necessarily derived from the first stage pyrolysis.

It may be desirable to exclude from the second stage feed stock heavy residual tar produced in the first stage.

Selected products produced in the second stage may be recycled with the second stage feed stock depending on the particular aromatic hydrocarbons, it is desired to produce. For example, if styrene is particularly desired, benzene, toluene and/or xylene produced in the second stage may be recycled therein.

The second stage may be carried out in the same or in difl'erent apparatus and for convenience willbe briefly described in connection with the apparatus of Figure 1.

The illustrative cycle of operation of the apparatus of Figure 1, as given in connection with stage one of the process may be repeated in all respects in connection with stage two of the process. I

However, the feed stock in stage two is preferably fed in through supply means l5, provided with nozzle l6, instead of through supply means l5b provided with nozzle lGb, although as in stage one the feed stock may be fed into the set at any other suitable point or points.

As previously pointed out a particularly preferred 'difierence between the operation of stage one and the operation of stage two is that in stage one in securing the desired intensity of pyrolysis, it is preferred to employ a combination of higher temperatures and shorter times of contact rather than to employ lower temperatures and longer times of contact to effect the same cracking intensity, while in stage two the reverse is the case,

As previously pointed out, having selected a suitable material for the second stage operation, its pyrolysis is controlled by the gas maker in such manner that the parafiine content of a fraction of the products of pyrolysis boiling between 107.5 C. and 112.5 C. and having a boiling range of 3 C. is less than 4% by volume and preferably in such manner that the parafiine content of a fraction of the products of pyrolysis having a boiling range of 1 C. and including 110.7" C., the boiling point of toluene, is as low as 1% by volume, determined as before described.

Should the parafilne content be too high, the operator should increase the intensity of cracking by the adjustment of one or more of the factors effecting the intensity of cracking.

Should the paraflinic content be lower than re- ,quired, the intensity of cracking may be decreased by the operator by the adjustment of one or more of the same factors.

While from the standpoint of quality of the desired aromatic hydrocarbon compounds, it may not be required to reduce the paraffin content of the 1 C. toluene fraction of the products of pyrolysis below 1% as determined by the above mentioned Kattwinkle test; it may be desirable to secure a further reduction of this parafline content as an effect of a higher intensity of pyrolysis required for the production of higher yields of certain aromatic compounds, for example, benzene and/or naphthalene. In such case the parafiine content of the above toluene fraction may be reduced to undeterminable proportions as measured by the above referred to Kattwinkle test or otherwise stated may be reduced to 0.2% or lower. For maximum yields of water gas benzene and naphthalene the intensity of cracking may be so increased that parafline content of said toluene fraction is zero as measured by the density method, that is the specific gravity of said 1" C. fraction including 110.7 C. may be that of toluene. *In fact maximum yields of benzene and/o1- naphthalene may be secured at higher intensities of cracking, than are required to reduce the paraffine content of said fraction to zero as measured by said density method.

The volume of residual oil gas referred to in the description of stage one may be calculated as follows:

Determination of residual oil gas The gas may be metered and sampled at any convenient stage in its condensation and purification, preferably however after purification from HzS. Water vapor is removed from a. measured portion of the sample and the Water vapor content ofthe gas calculated in per cent of the gas by volume, according to methods set forth in the Gas Chemists Handbook, 3rd edition, 1929, a publication of the American Gas Association, or their equivalent. The dried portion of the sample may be analyzed by low temperature fractionation as by means of the well known Podbelniak gas analysis apparatus or its equivalent. This apparatus has been described in Industrial and Engineering Chemistry, analytical edition, March 15, April 15, and May 15, 1933, and its use in hydrocarbon gas analysis is very well known to those skilled in the art.

By the above means, the dried sample may be divided into four portions: (1) containing H2, N2, 02, C0, C02, CH4, and any HzS, CS2, HCN, S02, NHs present, (2) containing C2 hydrocarbons such as C2H4 and CzHe, (3) containing C3 hydrocarbons such as CaHs and CsHa, and (4) containing C4 hydrocarbons and hydrocarbons of higher carbon content. The per cent by volume relationship of these portions of the original undried as may be readily calculated.

Another measured portion of the original sample may be analyzed for HzS according to methods described in the above mentioned Gas Chemists Handbook. From the analysis the percentage of E28 by volume in the gas as metered may be readily calculated.

Portion 1 may be analyzed for H2, N2, 02, CO and CO2, by means of the well known Hempel apparatus or its equivalent by methods described in the above mentioned Gas Chemists Handbook or their equivalents which methods include the initial removal of H25 and the percentage by volume of these constituents in the gas as metered calculated.

All of the N2, 02 and a portion of the CO2 are considered to be derived from air and combustion ases. The CO, the remainder of the CO2 and a portion of the H2 are considered to be derived from any water gas present. The remainder of the H2 is considered to be part of the oil gas. The method of apportionment of the CO2 between combustion gas and water gas and of the He between water gas and oil gas is as follows:

% N2 \I 0.80 O l +O 002 in combustion gases CO (C. G.) air and combustion gases= 2+% 2+ 02 Cog- 7 CO; (C. G.)=

. CO in water gas CO (W. G.) 2 CO (W. G.)+% CO= H in water gas: H; (W. G.) 00+ %H; (W. G.) CO; (W. G.)

The above apportionment of CO2 and H2 is known to be approximate as the percentages of CO and CO2 in water gas vary with the temperature of its generation. The approximation is however sufiiciently accurate for the purpose of calculating the residual oil gas.

The CS2, S02, HCN, and NH3 contents of the gas may be assumed to be negligible in the calculation of the residual oil gas unless these materials are known to be present in significant quantities which is usually not the case.

If the gas be metered and sampled after the usual H2S purification, the HzS may be assumed to be negligible for this calculation also, as the usual HzS purification removes practically all of the H23 as well as HCN and S02.

If the oil employed is not high in sulfur content, the H28 may be negligible for the calculation ofresidual oil gas even before H23 purification.

When employing low sulfur oils the H28 content of the gas prior to HzS purification may be of the order of 50 grains per 100 cu. ft., equivalent to approximately .08% by volume, which would be insignificant.

If a high sulfur oil is employed the H28 content of the gasprior to HzS removal might not be negligible in the calculation of residual oil gas and therefore if the gas be metered and sampled prior to H2S purification the H25 content should be determined and the volume of HzS deducted in calculating the residual oil gas.

From the volume of total gas in cubic feet as metered and the volume of oil pyrolyzed in its manufacture, in gallons, the cubic feet of total gas per gallon of oil under the pressure and temperature conditions of metering may be readily calculated. The volume of total gas per gallon of oil is for convenience called V1.

V1 X air and combustion gases=cubic feet of air and combustion gases per gallon of oil=V2 V1 x of water gas=cubic feet of water gas per gallon of il=V3 V1 X C4 hydrocarbons and higher=cubic feet of C4 hydrocarbons and higher per gallon of 0i1=V4 V1 water vapor=cubic feet of water vapor per gallon of 0i1=V5 V1 H2S=0ubiC feet of H23 per gallon of 0i1=Vc V1(V2+V3|V4+V5+V6) =cubic feet of residual oil gas per gallon of oil under the pressure and temperature conditions of metering=V1 If P=gas pressure as metered in mm. Hg and T=gas temperature as metered in F. absolute.

V X X =Residual oil gas in cubic feet per gallon of oil at a pressure of 760 mm. and a temperature of 60 F.

If the gas is metered and analyzed after the usual H2S purification Vs need not be deducted tity of C4 hydrocarbons left balanced-in great measure by the quantity of Ca hydrocarbons condensed.

Any suitable means may be employed for the condensation of hydrocarbon material, from the gas produced in the respective stages. The particular means selected will depend somewhat upon the diolefine material it is particularly desired to recover as a reuslt of a first stage operation and upon the particular portion or portions of the other first stage products which it is desired to employ as second stage feed stock.

The apparatus shown in Figures 2 and. 3 which figures when arranged end to end comprise a continuous flow sheet, may be conveniently employed for recovering hydrocarbon materials from the gas produced in either of the stages.

At the extreme left of Figure 2 is shown line l9 and wash box 4 together with gas outlet 20a and valve 2| of Figure 1.

As illustrated, outlet 20a leads to a multi-pass Wash box 4 is provided with a water supply 48 I and tar overflow 49 which leads to tar seal pot 50 to which as illustrated is connected a vapor outlet 5| leading to a condenser 52 for the recovcry of any vaporized material.

Tar fiowssfrom seal pct 50 through outlet 53 and may be drawn ofi separately through line 54 or may be combined through line 55 with the tar from the first vertical pass of condenser 4| which latter tar drains through line 56 into seal pct 51 with which line 55 connects. Seal pot 51 is provided with a vapor outlet 58 which may lead to a condenser (not shown) and with a, tar outlet 59.

Additional seal pots 6|, 62, 63, 64, 65, and 66 have been illustrated, each connected to a separate vertical pass of condenser 4| for the withdrawal of tar. Each of the seal pots may be constructed similarly to seal pct 51 including a vapor outlet with a condenser (not shown) and a tar outlet.

Gas cleaner 43 is also shown with a tar outlet 68 leading to seal pot 69 which also may be similar to seal pot 51.

The particular arrangement of seal pots 5D, 51, 6|, 62, 63, 64, 65, 66 and 69, each of which is provided with a separate tar outlet makes it possible to separately process the tar condensed at various points, if desired, or to combine the separate bodies of tar in any desired manner prior to processing. For example, the tar flowing from seal pots 50, 5|, and GI might be combined to form heavy tar, and the tar flowing from seal pots 62, 63, 64, B5, and 66 might be combined to form light tar.

It will be understood, of course, that any other suitable construction or arrangement or method of collecting tar might be substituted.

As illustrated, the condensate collected in drip pot 45 is drawn off through outlet H and since it is usually non-tarry in .nature, if desired, it may be combined with the light oil or otherwise processed, as desired.

Hydrocarbons also may condense within the relief holder 46 and if so may be skimmed off of the top of the water through drain 12. This condensate is usually non-tarry in nature and i of the nature of light oil. Therefore, if desired,

17 it may be combined, for example, with similar or lighter condensate and processed therewith.

Relief holder 48 is illustrated with the conventional water inlet 13 for replacing water losses from the tank thereof.

Relief holder 46 is shown with gas outlet 15 which leads through drip pot I6 and line 11 to the gas purifier system illustrated generally at I8 and more specifically as containing iron oxide boxes I9 and 80, although it is to be understood that any suitable gas purifier system may be substituted. The connections to the purifier boxes 19 and 80 are conventional and will, therefore, not be more particularly described.

Purifier boxes 19 and 80 are illustrated with drip pots 8i and 82 respectively for the collection and removal of condensate.

Outlet 84 from the purifier system 18 leads through gas meter 85 and past thermocouple junction 88 which is connected to pyrometer 81 for measuring the gas temperature. Gas pressure guage 88 is also provided.

The purpose of meter 85, pyrometer 8i and pressure guage 88 is to furnish data for calculating the volume of gas flowing through outlet 84.

If residual oil gas" is to be calculated from thi data a sample of the gas for analysis should be taken at this point.

Since condensation may occur in outlet 84, a drip pot 89 is illustrated in this outlet. It is to be understood that a drip pot or drip pots may be placed at any other point or points in the system for the collection and removal of condensate.

As illustrated, outlet 84 leads to compressor 9I driven by a prime mover 92, the gas passing through compressor 9 I, then through after-cooler 93, through a second compressor 94, after-cooler 95, a third compressor 96, after-cooler 91', and through line 98 to a scrubbing tower 99. Each of the after-coolers 93, 95 and 97 is illustrated as provided with condensate drains IOI, I02, and I03 respectively which as illustrated are connected to a common line I04 to be referred to again hereinafter. The after-coolers may be of any suitable design and operation.

Each of the compressors 94 and 96 is also illustrated as driven by a prime mover 92.

Any other means may be provided for raising the pressure of the gas and for abstracting heat therefrom for the purpose of producing condensate.

Generally speaking, the pressure in the system from wash box 4 to and through outlet 84 is conveniently slightly above atmospheric. The pressure in outlet 98 may be as desired, for example, in the particular system illustrated conveniently of the order of from 200 to 225 pounds per square inch absolute.

The temperature of the gas in outlet 84 may be maintained at any desired level, such as between 90 F. and 100 F. Reference is made to copending application Serial No. 301,330, filed October 26, 1939, by Edwin L. Hall. Th temperature of the gas in outlet 98 may also be as desired, for example, conveniently of the order of from 85 to 100 F.

As illustrated outlet 98 is connected to the bottom of scrubber 99, the gas passing up through scrubber 99 countercurrently to a liquid gasscrubbing medium of considerably lower vapor pressure such as a scrubbing oil. The scrubbing medium enters scrubber 99 through line I05 which leads from the bottom of stripping tower II4 through cooler I06 to the top of scrubber 99. The proportion of scrubbing oil to gas and the temindispensable essential.

The eflluent gas is led through gas meter I08, past thermocoupl junction I09 leading to pyrometer II 0, and past pressure gauge III. A purpose of meter I08, pyrometer H0 and pressure gauge III is to determine the volume of eiiluent gas for purposes of calculating residual oil gas," provided residual oil gas" is calculated from the analysis of gas sampled at this point.

It will of course be understood that even though a substantial portion of hydrocarbons of less than 4 carbon atoms were condensed it would, nevertheless, be possible to calculate residual oil gas as herein defined, by adding to the residual oil gas as determined from the sample a volume to compensate for such condensation.

Returning to scrubber 99, scrubbing medium containing condensate is withdrawn through line H3, through heater I25, and fed to the top of stripper H4 in which condensate scrubbed from the gas in scrubber 99 is stripped from the scrubbing medium such as with the aid of live superheated steam introduced through line H2. The stripped material is taken overhead through line II5 to and through condenser I I6 which leads to decanter I I1 and the scrubbing medium is returned through line I05 and cooler I06 to scrubber 99, any makeup being added as required.

Decanter H1 is conveniently provided for the separation of condensed water and of any gas remaining uncondensed after passing through condenser H8. Uncondensed gas is led through line II8 back to line 84 and is thus recycled through the compressors.

Line I04 conveniently leads to decanter II! in which condensate from after-coolers 98, and 91 is combined with condensate from condenser H6.

Any water collecting in decanter II! is drained off through line H9, and hydrocarbon condensate is drained off through line I20 into fractionating tower I2I. A separation is made between higher and lower boiling hydrocarbon components in tower I2I, for example, between hydrocarbons of 6 carbon atoms and higher which are taken off in the liquid phase at the bottom through line I 22,v and hydrocarbons of less than 6 carbon atoms which are taken off in the vapor phase through line I23. The latter are condensed, a part returned to tower I2I as reflux, and the rest led to fractionating tower I24 in which a separation is made between hydrocarbons of 5 carbon atoms and higher which are taken off in the liquid phase through line I26, and hydrocarbons of less than 5 carbon atoms which are taken oil in the vapor phase through line I 21. The latter are condensed, a part returned to tower I24 as reflux, and the rest led to suitable apparatus for the recovery of hydrocarbons with 4 carbon atoms (not shown).

The unsaturated diolefine hydrocarbons of 5 carbon atoms, namely, isoprene, piperylene, and cyclopentadiene may be separated from each other by any available means such as by the processes described and claimed in Patent 2,211,038,

19 granted August 13, 1940, to Alger L. Ward, and in copending application Serial Number 342,910, filed June 28, 1940, by Alger L. Ward, which has matured into Patent No. 2,397,580, granted April 2, 1946.

The unsaturated hydrocarbons of 4 carbon atoms, namely, butadiene and the butylenes may also be separated from each other by any available means such as by the processes described in the literature including granted patents.

The employment of the above described apparatus permits a ready separation from the condensate of a very wide variety of individual hydrocarbons,

With respect to the condensate from first stage operation, all of this condensate with the exception of the desired diolefine material to the production of which the first stage is particularly directed, may be employed in admixture as feed stock for the second stage operation.

It is preferred not to employ any considerable proportion of the C4 and C5 dioleflne material produced in the first stage as second stage feed stock, and particularly it is preferred not to so employ any considerable proportion of the first stage butadiene.

Inasmuch as steam is preferably employed as a diluent in the first stage, and inasmuch as at least in cyclic operations the products of pyrolysis are contacted with water in the wash box, at least a portion of the condensate is frequently recovered in the form of an aqueous emulsion, which is preferably broken prior to use of the material as second stage feed stock. This emulsion may be broken by any convenient method known to the art.

It may be preferred to employ only "a portion 01' the condensate remaining after the separation of the desired diolefine material as second stage feed stock, and in such case it may be found convenient to divide this remaining condensate into light oil, dead oil, and residual tar, from which the desired second stage stock may be selected. If such a separation into dead oil, light oil, and residual tar is effected, the dehydration of the tar emulsion may be conveniently effected at the same time.

The condensate collected from the various drip pots and from the holder 48 is usually not in the form of an emulsion. This. condensate if desired, may be combined with the condensate fed to tower I 2|. On theother hand, this material may be combined with light oil separated from the original tar.

Light oil recovered from the tar and the condensate from the drip pots, and the holder, and the heavier hydrocarbon material se arated in tower PM may contain benzene, alkylated benzene. such as toluene, and the xylenes, resinforming unsaturated aromatic hydrocarbons such as styrene, the methyl styrenes, and indene as well as other valuable hydrocarbon material, such as dicyclopentadiene.

This combined light oil constitutes an excellent feed stock for sta e 2 of the Process.

It may be preferred, however, to eflect a separation of this light oil to recover fractions in which individual hydrocarbons or groups of hydrocarbons are concentrated, and to select one or more of such fractions as feed stock for stage 2. For example, an excellent feed stock is a fraction having a boiling range including the boiling points of benzene,'toluene, and the xylenes, and in which C6 to Ca hydrocarbons are concentrated.

Hydrocarbon material not contained in the 20 particular fraction or fractions employed as sec- 0nd stage feed stock may be separately concentrated and recovered if desired.

With respect to the removal of hydrocarbon material from the gas produced in the second stage operation, the degree of condensation em ployed may depend somewhat upon the particular feed stock employed in the second stage and the particular intensity of pyrolysis employed therein. For example, under certain conditions of second stage operation, it may not be economical to condense from the gas materials containing a lesser number of carbon atoms per molecule than six or perhaps 5, since the treatment may be such as not to favor the formation or the survival of such C4 and C5 compounds as butadiene, isoprene, piperylene, and cyclopentadiene.

On the other hand, under the milder pyrolysis conditions within the scope of the second stage operation, suflicient quantities of such valuable Cr/and C5 hydrocarbons may be present in the second stage products of pyrolysis to well warrant recovery.

The products of pyrolysis of six carbon atoms and more which are present in the condensate from the second stage operation, may be separated for the recovery of the desired individual aromatic hydrocarbon compounds by any convenient means known to the art. Inasmuch as the presence of a diluent in the second stage pyrolysis environment is not necessarily desirable and inasmuch as in continuous operation the products may not come in contact with water in condensation, the second stage tar may not be in the form of an emulsion. If such is the case, of course no dehydration step is necessary. If, however, a substantial quantity of steam diluent is employed or if the products come in contact with water during condensation with the formation of an emulsion, the said emulsion may be broken by any convenient method known in ,the art and preferably by a method which avoids the polymerization of readily heat polymerizable unsaturated aromatic hydrocarbons boiling above 210 (3., which may be present in relatively high concentration in the higher boiling condensate.

This dehydration may be readily effected coincidentally with the separation of the tar into light and dead oil, and residual tar.

The light oil from the second stage operation is a source of a variety of aromatic hydrocarbons, both those containing only nuclear and those containing other than nuclear unsaturation and which may be recovered therefrom in a high degree of purity, particularly with respect to paraflinic contamination,

The yields of individual aromatic hydrocarbons having boiling points within the light oil range (up to approximately 210 C.) will depend to a great extent upon the particular intensity of cracking employed in the second stage pyrolysis. Relatively mild cracking conditions within the range of second stage pyrolysis intensities will generally result in higher yields of such aromatic compounds as the xylenes and methyl styrenes. Relatively more severe cracking conditions favor the higher yields of such aromatic compounds as styrene toluene, and indene, while still more severe cracking intensities favor the higher yields of such aromatic compounds as benzene and naphthalene. Therefore, while all of these 'compounds may be recovered from second stage operation in high quality, the relative yields may be varied as desired.

Added aromatic hydrocarbon material may be advantageously employed with the first stage products as second stage feed stock. For ex,- ample, if high yields of xylene, toluene and styrene, particularly the latter are desired, benzene produced in, the second stage or from any other source may be admitted to any desired portion of the pyrolyzing path during the pyrolysis. Other added hydrocarbon material of aromatic or other character may be employed.

' As before stated, such aromatic compounds as benzene, toluene and xylene may be recovered from the second stage in high purity from a standpoint of parafline contamination and after acid washing may be entirely suitable for nitration. Due to low content of aliphatic olefines in the aromatic fractions, high acid wash losses may be avoided.

The two-stage process of theinvention, in the second stage thereof, also favors the production of high boiling aromatic compounds of unusual value. These compounds will 'be found in the dead oil boiling range, that is above approximately 210 C., particularly above 250 C., and even above 300 C.

These compounds comprise unsaturated aromatic hydrocarbon material, a large proportion of which is readily heat polymerizable to form valuable resins. This portion of the unsaturated :liydrocarbon material may be also catalytically polymerized. Another portion of this unsaturated material is not readily polymerizable by heat, but is readily polymerizable by the aid of catalyst.

Also contained in the dead oil from the second stage operation are valuable non-resin-forming aromatic hydrocarbon materials which have great value as high boiling solvent aromatic oils.

The second stage operation is admirably suited for the production of dead oil of the character aboye'described of very high aromaticity as indicated by such criteria as aniline number.

Further, the residual tar which may be produced from the second stage condensate may have much greater than fuel value.

Instead of employing a cyclic operation in apparatus such as that of Figure 1, a continuous or continual operation may beemployed.

Referring now to Figure 4 wherein cracking apparatus of the continuous or continual type is illustrated, I comprises a reaction tube which may be any material suitable for continuous or continual cracking operations.

Tube I45 at its inlet I46 is shown provided with a baflle I" in the form of a cup into which project hydrocarbon feeding tube I48 and steam feeding tube I49. Feeding tubes I48 and I49 pass through and form a gas-tight fit with a closure member I50 for the inlet end of tube I45.

Tube I45 adjacent its outlet end I5I is provided with a gas delivery side arm I52 and a closure member I53, the latter being sufliciently below side arm I 52 to form a well I 54.

Tube I45 is also shown provided with an axially arranged tube I of smaller diameter. Tube I55, as shown, projects through closure member I50 and I 53- and provides a convenient way of arranging thermocouple junctions for the measure of temperature. Tube I55 may be of any convenient material suitable for continuous or continual cracking purposes.

Tube I 45 may be of any convenient length which is usually correlated with the provisions for feeding steam and for feeding and vaporizing oil and any additive in order to make it possible to obtain any desired times of contact.

. 22 For temperature control purposes, tube I 45 is shown surrounded with a heating member I51 in the .form or a resistance winding which may be provided with several taps, as illustrated I58;

I45 as well as to vary such conditions along tube I45, if and as desired.

Assuming that heaters I51 and I and cooler I59, if necessary, are operating to establish desired temperature conditions within tube M5, the operation of the apparatus shown in Figure 4 is as follows:

Hydrocarbon feed stock is fed through tube I48 and steam or other diluent is fed through tube I49. These materials strike bafile I4I thus becoming mixed. The resulting reduction in partial pressures of hydrocarbon vapors and the surrounding temperatures are ordinarily suilicient to vaporize all of the hydrocarbons present.

The vaporized hydrocarbons in passing through tube I45 in the presence of steam or other diluent are pyrolyzed in a manner similar to that already described in connection with Figure 1,

Because of the pyrolysis conditions involved,

by far the bulk of the materials except very de-- hydrogenated material such as free carbon remain in the vapor phase and pass oil through delivery arm I52 with th gas. The tar and lower boiling condensates may be separated from the gas in any desired manner, for example as described in connection with he first stage or second stage operation of Figure 1, depending upon which stage of pyrolysis is being conducted in the apparatus of Figure 4.

As particularly described, the portion of the tube I45 above the cooling coil I59 usually constitutes the chief pyrolyzing chamber, and the portion of the tube below the cooling coil I59 is usually maintained at a temperature sufliciently high to avoid condensation of heavy tars whether or not such temperature is sufliciently high to substantially prolong the pyrolysis.

If desired, tube I45 may contain refractory material of suitable size and shape, particularly if sufficient free space is afforded for the flow of vapors, such additional refractory materials providing additional contact'surfaces.

Any other heating means may be added or substituted.

Small amounts of free carbon or other nonvaporizable substances tend to collect in well I54 from which they may be removed during cleaning by removal of closure member I53.

When the walls of tube I45 become coated with a layer of carbon sufilciently thick to interfere with proper heat exchange, or otherwise, it may be removed by any suitable means, such as by passing air or oxygen in through tube I48 or I49, or both, the products of combustion being removed through side arm I52.

Control Of such factors as heating, velocity of hydrocarbon materials and diluent through the apparatus, together with the quantity and character of diluent employed permits the operator to secure the desired pyrolysis conditions which satisfy the above recited criteria for either first or second stage operation.

The same condensing apparatus may be employed if desired in connection with the apparatus of Figure 4 as in connection with the apparatus of Figure 1. Due to the continuous operation, however, the wash box land the relief holder 46 of Figure 2 may be omitted, if desired. when this apparatus is employed to condense the products of the pyrolyzing apparatus of Figure 4.

While a wide variety of hydrocarbon material may be pyrolyzed together with the petroleum oil in the first stage, it is preferred to avoid the addition of benzene or butadiene, or at least to avoid the addition of more than a small proportion thereof, which should be subtracted from the total benzene and/or butadiene produced, before calculating the benzene-butadiene ratio, hereinbefore referred to.

In referring to preferred temperature conditions of pyrolysisin the respective stages, average temperatures of the pyrolyzing path or zone are intended.

In referring to preferred time of contact in connection with first and second stage Py olysis, it is intended to mean time of contact as calculated in the following arbitrary manner.

The average volume per unit time of the vaporized, but entirely uncracked, hydrocarbon feed stock at the temperature and pressure of the inlet end of the pyrolyzing path or zone, to-' gether with the average volume per unit time of any accompany diluent at said temperature and pressure may be calculated in cubic feet per sec. from average input rates and the aver age molecular weights of said feed stock and diluent, if any.

The average volume per unit time of the products of pyrolysis at the end of the pyrolyzing path or zone and at the temperature and pressure of the end of the pyrolyzing path or zone may be calculated in cubic feet per second from the measurement of the flow of the gas in cubic feet per unit time at any stage in the condensation together with measurement of the total quantity per unit time and the average molecule weight of the condensate from the gas up to and including the condensation stage, at which the gas is measured.

The arithmetical average of the average volume in cubic feet per second of the vaporized but uncracked hydrocarbon feed stock and diluent, if any, at the beginning of the pyrolyzing path or zone and at the pressure and temperature thereof, and the average volume in cubic feet per second of the products of pyrolysis and diluent, if any, at the end of the pyrolyzing path or zone at the temperature and pressure thereof divided into the free space in cubic feet of the pyrolyzing path or zone equals the time of contact in seconds.

It will, of course, be understood, that in the event that material, whether hydrocarbon feed stock or diluent, is fed in or in the event that products and diluent, if employed, are led off intermediate the ends of the pyrolyzing path, due account is to be taken of the shorter travel of such material in the pyrolyzing environment and the different average temperature and pressure to which it may be exposed as a result thereof.

The time of contact employed is intended to be an arbitrary average time of residence in the pyrolyzing environment of the hydrocarbon material pyrolyzed and the products of pyrolysis, which of course is influenced by the presence or absence of diluent, other things being equal.

With respect to gauge pressures in the pyrolyzing environment. any convenient gauge pressure such as in the neighborhood of or atmospheric pressure may be employed in either stage. However in the first stage relatively low auge pressures may be preferred, while in the second stage the preference may be for relatively high gauge pressures. Thus in the first stage it may be preferred to maintain pressure conditions not over 60 pounds per square inch gauge, more preferably not over 30 pounds per square inch gauge and still more preferably pressures below atmospheric. Further, in second stage it may be preferred to maintain pressure conditions of at least three quarters of an atmosphere absolute, more preferably at least 100 pounds per square inch gauge and still more preferably at least 200 pounds per square inch gauge. It will be understood by those skilled in the art that the apparatus employed may be modified as may be necessary for the particular pressure conditions selected.

A wide variety of petroleum oils may be employed in the present invention. The naphthenic oils such as those of classes 5 to 7, according to the method of classification of Bureau of Mines Bulletin 291 as modified by Bureau of Mines Report of Investigation 3279, generally hav the advantage of a more facile production of aromatic compounds of good quality, while the more paramnic oils such as those of classes 1 to 4 by the same method of classification generally have the advantage of a more ready production of high yields of diolefines.

It is to be understood that in the second stage of the pyrolysis, the reduction of the paramnic contamination of the aromatic hydrocarbons, also reduces the aliphatic olefine content of the aromatic hydrocarbon fractions. The oiefinic contamination is not as serious as the paraflinic contamination, in that it may be removed more readily as by acid washing. In as much, however, as acid washing of the aromatic fractions is accompanied by wash losses of the aromatic hydrocarbons, the reduction of the olefine contamination is a decided advantage. The wash losses that would be incurred in removing olefines from,

for example, fractions embracing the boiling point of benzene and produced under pyrolysis conditions yielding maximum butadiene may be so high as to be prohibitive.

Many modifications of the forms of the invention-illustratively described above may be made.

For example, while either continuous pyrolysis or cyclic pyrolysis may be employed in both stages, one of these general types of pyrolysis may be employed in either stage, while the other general type is employed in the other stage. For example, a continuous tube cracking apparatus may be advantageously employed in the first stage with pyrolysis conditions of mild intensit which develop little free carbon, while cyclic regenerative apparatus may be employed in the second stage in which more free carbon may be developed, but which may be prevented from accumulating by the combustion carried on during the air blasting periods of the cycle.

On the other hand, cyclic operation may be employed in the first stage with con inuous tube cracking in the second stage, the latter being generally more convenient if high pressures are desired in the second stage operation.

Further, the particular feed stocks employed may influence the choice of continuous or cyclic pyrolysis.

As another modification, either stage whether continuous or cyclic may operate on prevaporized feed stock.

Therefore, changes, omissions, additions, substitutions, and/or modifications may be made within the scope oi the claims without departing from the spirit of the invention.

I claim:

1. A process comprising passing petroleum oil in vapor phase through a heated pyrolyzing path and pyrolyzing said oil therein in the presence of a diluent gas to produce conjugated dioleflne material oi. from 4 to carbon atoms including butadiene and aromatic hydrocarbon' material including benzene and with an intensity of pyrolysis at least suiiicient to cause the production of at least 20 cubic feet oi residual oil gas per gallon of oil pyrolyzed and insuflicient to cause the ratio oi the total benzene produced per gallon of oil to the total butadiene produced per gallon of oil to be greater than 2 to 1, thereby unavoidably producing parafilne material of boiling point similar to that of said aromatic hydrocarbon material, separating conjugated diolefine material of from 4 to 5 carbon atoms from the resulting products of said pyrolysis, thereafter subjecting at least a portion of the products of said pyrolysis remaining after said separation and containing said aromatic hydrocarbon material an parafline material of similar boiling point to vapor phase pyrolysis in a second pyrolyzing path under pyrolytic conditions of such intensity that an olefine free fraction separated from the products of said second pyrolysis and having a boiling range of 3 C. included between 107.5 C. and 112.5 C. has a parafllne content of less than 4% by volume, and separating from said products of said second DY- rolysis aromatic hydrocarbon material relatively free from paraffinic contamination of similar boiling point.

2. A process comprising passing petroleum oil in vapor phase through a heated pyrolyzing path and pyrolyzing said oil therein in the presence of steam to produce conjugated diolefine material of from 4 to 5 carbon atoms including butadiene and aromatic hydrocarbon material including benzene and toluene and with an intensity of pyrolysi at least suflicient to cause the production'of at least 20 cubic feet of residual oil gas per gallon of oil pyrolyzed and insuilicient to cause the ratio of the total benzene produced per gallon of oil pyrolyzed to the total butadien produced per gallon of oil pyrolyzed to be greater than 2 to 1, thereby unavoidably producing aromatic hydrocarbon material contaminated with parafllne material of similar boiling point, separating conjugated diolefine material of from 4 to 5 carbon atoms from the resulting products of said pyrolysis, thereafter subjecting at least a portion of the products of said pyrolysis remaining after said separation and containing aromatic hydrocarbon material including toluene contaminated with a relatively high proportion of parafline ma.. terial of similar boiling point to vapor phase pyrolysis in a second pyrolyzing path under pyrolytic conditions of such intensity that an olefine free fraction separated from the product of said second pyrolysis and having a boiling range of 1 C. including 110.7 C. has a parafflne content of less than 1% by volume, and separating aromatic hydrocarbon material from said products of second stage pyrolysis substantially free from parafline material of similar boiling point.

3. A stage-wise process for the production of conjugated diolefine material of from 4 to 5 carbon atoms including butadiene and aromatic hydrocarbon material having less than 9 carbon atoms including benzene and toluene, said aromatic hydrocarbon material being relatively free from paramne contamination of similar boiling point comprising subjecting petroleum oil in a first pyrolyzing stage in the presence of steam in proportion of at least 1 part oi. steam to 2 parts of petroleum oil by weight to thermal decompositionin vapor phase to produce butadiene and said aromatic hydrocarbon material, said thermal decomposition being of sufllciently high intensity to cause the formation of at least 25 cubic feet oi residual oil gas per gallon of petroleum oil pyrolyzed and insufiiciently high to cause the ratio of the total benzene produced per gallon of petroleum oil pyrolyzed to the total butadiene produced per gallon of petroleum oil pyrolyzed to be greater than 1.5 to 1, thereby producing aromatic hydrocarbon material unavoidably contaminated with relatively high proportions of parafline material of similar boiling point, separating conjugated dioleflne material of from 4 to 5 carbon atoms including butadiene from the products of said pyrolysis, subjecting to further pyrolysis in vapor phase in a second pyrolyzing stage a portion of said products of said first pyrolysis remaining after said separation of butadiene, said portion including aromatic hydrocarbon material boiling between 60 C. and 165 C. contaminated with parafline material of similar boiling point, said further pyrolysis in said second pyrolyzing stage being conducted in the presence of at least 0.4 part of steam per part of said portion of said products by weight and with an intensity such that an olefine free fraction separated from the products of said second pyrolysis and having a boiling range of 1 C. including 110.'I C. has a parafline content of less than 1 by volume, and separating from said products of said second stage pyrolysis aromatic hydrocarbon material boiling within the range from 60 C. to C. and substantially free from paraffine material of similar boiling point.

4. A stage-wise process for the production of conjugated diolefine material of from 4 to 5 carbon atoms including butadiene and aromatic hydrocarbon material of less than 9 carbon atoms including benzene and toluene and relatively free from parafiinic contamination of similar boiling point comprising subjecting petroleum oil in a first pyrolyzing stage in the presence of at least 1 part of steam to 1 part of petroleum oil by weight to thermal decomposition in vapor phase under average temperature conditions between 1400 F. and 1800 F. to'produce conjugated diolefine material of from 4 to 5 carbon atoms including butadiene and aromatic hydrocarbon material of less than 9 carbon atoms including benzene, said thermal decomposition being of sufilciently high intensity to cause the formation of at least 25 cubic feet of residual oil gas per a gallon of petroleum oil pyrolyzed and insufficiently high to cause the ratio of the total quantity of benzene produced per gallon of petroleum oil pyrolyzed to the total quantity of butadiene produced per gallon of petroleum oil pyrolyzed to be greater than 1.5 to 1, thereby producing aromatic hydrocarbon material of less than 9 carbon atoms including benzene and toluene unavoidably accompanied by a relatively high paraffine contamination of similar boiling point, separating conjugated diolefine material oi? from 4 to 5 carbon atoms including butadiene from the products of said first stage pyrolysis, subjecting to further pyrolysis in vapor phase in a second pyrolyzing stage a portion oi said products of said first stage pyrolysis remaining after said separation of conjugated diolefine material, said portion including aromatic and parafilnic hydrocarbon material boiling between 60 C. and 165 C. and said further pyrolysis being conducted in the presence of less than 1 part of steam by weight to 1 part of said portion of said first stage pyrolysis products pyrolyzed and with an intensity of pyrolysis such that an olefine-free fraction separated from the products of said second pyrolysis and having a boiling range of 1 C. including 110.7 C. has a parafiine content of less than 1% by volume, and separating from said products of said second stage pyrolysis aromatic hydrocarbon material boiling between 60 C. to 165 C. and substantially free from paraffine material of similar boiling point.

5.. A stage-wise process for the production of conjugated diolefine material of from 4 to 5 carbon atoms including butadiene and aromatic hydrocarbon material having less than 9 carbon atoms including benzene and toluene, said aromatic hydrocarbon material being relatively free from paraifinic contamination of similar boiling point comprising subjecting petroleum oil in a first pyrolyzing stage in the presence of a proportion of steam at least as great as 1 part of steam to 1 part of petroleum oil pyrolyzed by weight to thermal decomposition in vapor phase under average temperature conditions between 1400 F. and 1800" F. to produce conjugated diolefine material of from 4 to 5 carbon atoms including butadiene and aromatic hydrocarbon material of less than 9 carbon atoms including benzene and toluene, said thermal decomposition being of sufiiciently high intensity to cause the formation of at least 25 cubic feet of residual oil gas per gallon of petroleum oil pyrolyzed and insufficiently high to cause the ratio of the total quantity of benzene produced per gallon of petroleum oil pyrolyzed to the total quantity of butadiene produced per gallon of oil pyrolyzed to be greater than 2 to 1, thereby producing aromatic hydrocarbon material of less than 9 carbon atoms including benzene and toluene unavoidably accompanied by a relatively high proportion of parafiine material of similar boiling point, separating conjugated diolefine material of from 4 to 5 carbon atoms including butadiene from the products of said first stage pyrolysis, subjecting to further pyrolysis in a second pyrolyzing stage a portion of said products of said first pyrolysis remaining after said separation of said conjugated diolefine material, said portion including aromatic and parafiinic hydrocarbon material boiling between 60 C. and 165 C., said further pyrolysis being conducted in a cyclic operation in which during a heating period of the cycle a path of storedheat is established by the passage of hot combustion gases in contact with refractory heat storage material arranged along said path and in which in a petroleum oil pyrolysis period of said cycle said portion of said products of said first pyrolysis is pyrolyzed by passage in vapor phase along said path of stored heat, said second pyrolysis being conducted in the presence of diluent steam and with an intensity of pyrolysis such that an olefine-free fraction separated from the products of said second pyrolysis and having a boiling range of 1 C. including 110.7" C. has a parafiine content of less than 1% by volume, and separating from said products of said second stage pyrolysis aromatic hydrocarbon material boiling within the range of 60 C. to C. and substantially free from v paraffine material of similar boiling point.

6. In the process of claim 5 the steps or conducting the first stage pyrolysis with an average time of contact less than 1 second and conducting the second stage pyrolysis under average temperature conditions less than 1600 F., with an average time of contact of more than 1 second and with a steam dilution at least as low as 1.0 part of steam per part of said products of first stage pyrolysis pyrolyzed by weight.

7. In the process of claim 5 the steps of conducting the first stage pyrolysis of petroleum oil in the presence of a proportion of steam at least as great as 3 parts of steam by weight to 2 parts of petroleum oil pyrolyzed, conducting said first stage pyrolysis with an average time of contact of less than 1 second, and with an intensity insufiiciently high to cause the ratio of the total quantity of benzene produced per gallon of petroleum oil pyrolyzed .to the total quantity of butadiene produced per gallon of petroleum oil pyrolyzed to be greater than 1.5 to 1, and conducting said second stage pyrolysis under average temperature conditions less than 1600 F. and with an average time of contact of more than 1 second.

8. A process for the production of conjugated diolefine material of from 4 to 5 carbon atoms including butadiene and aromatic hydrocarbon material of less than 9 carbon atoms including benzene and toluene, and aromatic hydrocarbon material being substantially free from parafiine material of similar boiling point which comprises pyrolyzing petroleum oil in vapor phase to produce conjugated diolefine material of from 4 to 5 carbon atoms including butadiene and aromatic hydrocarbon material of below 9 carbon atoms including benzene and toluene, said pyrolysis being conducted in the presence of from 1 to 4 parts by weight of steam per part of petroleum oil pyrolyzed and under average temperature conditions between 1400 F. and 1800 F. and with an average time of contact between 1 second and 0.1 second and with an intensity of pyrolysis sufficient to produce at least 20 cubic feet of residual oil gas per gallon of petroleum oil pyrolyzed but insufficient to cause the ratio of the total quantity of benzene produced per gallon of petroleum oil pyrolyzed to the total quantity of butadiene produced per gallon of petroleum oil pyrolyzed to be more than 2 to 1, removing conjugated diolefine material of from 4 to 5 carbon atoms from the resulting products of pyrolysis, thereafter subjecting at least a portion of the remaining products of said pyrolysis containing aromatic hydrocarbon material boiling between 60 C. and 165 C. together with parafiine contamination of similar boiling point to thermal decomposition in vapor phase in a second pyrolysis stage in the presence of not more than 1 part of steam by weight to 1 part of said products of pyrolysis so subjected to pyrolysis in said second stage, and conducting said second stage pyrolysis under average temperature conditions less than 1600 F. and with an average time of contact between 1 and 8 seconds and with an intensity of pyrolysis sufficiently high so that an olefine free fraction separated from the products of said second pyrolysis and having a boiling range of 1 C. including 1l0.7 C. has a parafline content of less than 1% by volume, and separating from the products of said second stage pyrolysis aromatic hydrocarbon material boiling between 60 C, and

165' C'. and substantially free from parafline material of similar boiling point.

9. A process according to claim 8 in which at least the second stage pyrolysis is conducted in a cyclic operation in which during a heating period of the cycle heat is stored in a path oi. stored heat by the passage of combustion gases in contact with refractory heat storage material arranged along said path and in an oil pyrolyzin period of the cycle the stored heat is employed for pyrolysis by the passage of the material to be pyrolyzecl in vapor phase along said path.

10. In a process for the production of valuable resin-forming unsaturated hydrocarbon material including diene material of less than 6 carbon atoms at least some of which is in the form of butadiene and aromatic resin-forming material involving the vapor phase pyrolysis of petroleum oil, the steps oi. favoring increased recoveries 012-- said diene material including butadine and said aromatic resin-forming material which comprised conducting said pyrolysis under temperature conditions between 1400 F. and 1800 F. in the presence of a quantity of diluent gas at least equivalent to the volumetric dilution produced by the employment of 1 part of steam to 2 Parts petroleum oil by weight thereby producing products of pyrolysis containing diene material including butadiene and containing other normally gaseous unsaturated hydrocarbon material, separating the greater part of said diene material including the greater part of said butadiene from said products or pyrolysis, and recovering residual gas containing normally gaseous olefinic material and relatively free from butadiene, thereafter pyrolyzing said residual gas in the presence of benzene in a second pyrolyzing environment, thereby producing aromatic hydrocarbon material including aromatic resin-forming hydrocarbon material, and separating said aromatic resin-forming hydrocarbon material from the products of said second pyrolysis.

NEWCOMB K. CHANEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Groll et al., Jour. Ind. Eng. Chem. vol. 25, 784-797 (1933). (Pat. Ofi. Lib.)

Dobryanskii et al., Transactions of the Research Plant Khimgazj' Materials on Cracking v and Chemical Treatment of Cracked Products, vol. 2, -97 (1935). (Photostat of Translation in 260-680), 34 pages.

Lebedev et al., Oil and Gas Journal, Feb. 11, 1943, 61, 63-, 65, 67, and February 25, 1943, 76, 78, 79, 81. (Pat. Oil. Lib.)

Tropsch et al., Jour. Ind. Eng. Chem., vol. 30, 169-172 (1938). (Pat. Oil. Lib.) 

